The present invention relates to an information storage medium represented by a large-capacity optical disc and a digital information recording/playback system using the medium.
In particular, the present invention relates to a DVD (digital versatile disc) recording/playback system that considers real-time recording of a moving picture.
The present invention also relates to a recording/playback system which can guarantee continuous playback (or continuous recording) upon continuously playing back (or continuously recording) information using playback devices (disc drives) having various access performances.
Furthermore, the present invention relates to a recording/playback system which can prevent any playback timing errors of video information and audio information recorded on the medium.
1. Description of Prior Art
In recent years, systems for playing back the contents of optical discs that have recorded video (moving picture) data, audio data, and the like have been developed, and have prevailed for the purpose of playing back movie software, karaoke, and so on like LDs (laser discs), video CDs (video compact discs), and the like.
Among such systems, a DVD (Digital Versatile Disc) standard that uses MPEG2 (Moving Picture Experts Group) international standard, and adopts an audio compression scheme such as AC-3 (digital audio compression) or the like has been proposed. The DVD standard includes read-only DVD video (or DVD-ROM), write-once DVD-R, and erasable/rewritable DVD-RW (or DVD-RAM).
The DVD video (DVD-ROM) standard supports MPEG2 as a movie compression scheme, and AC3 audio and MPEG audio in addition to linear PCM as an audio recording scheme, in accordance with MPEG2 system layer. Furthermore, this DVD video standard is configured by appending sub-picture data for superimposed dialogs obtained by runlength-compressing bitmap data, and control data (navigation data) for playback control such as fastforwarding, rewinding, data search, and the like.
Also, this standard supports ISO9660 and UDF Bridge format to allow a computer to read data. Hence, a personal computer environment can handle video information of DVD video.
2. Problem
However, a personal computer system and DVD recording/playback system use different appropriate information processing methods, and it is difficult for the personal computer to record/play back movie information for a long period of time continuously (without being interrupted).
More specifically, in the personal computer environment, when file data is to be changed, a process for re-recording the entire changed file data on a free area of an information storage medium (HDD or the like) is done. At this time, the re-recording position on the information storage medium is determined irrespective of the file data recording position before change. The file data recording position before change is released as a small free area after the change. If such change of file data is frequently repeated, small free areas are scattered in a vermicular pattern at physically separated positions on the medium. As a result, upon recording new file data, that data is recorded on a plurality of vermiculated free areas while being fragmented. This state is called fragmentation.
In the information process of the personal computer, information (file data) used is readily scattered (fragmented) on the disc. Even when a file to be read out has been fragmented, required information can read out from a disc by sequentially playing back such fragments recorded randomly. This fragmentation slightly prolongs the required read-out time of a file, but the user does not feel disrupted if a high-speed HDD is used.
However, when recorded information (MPEG-compressed moving picture data) has been fragmented in a DVD recording/playback system, if such fragments recorded randomly are to be played back in turn, moving picture playback may often be interrupted. Especially, since an optical disc drive requires a longer seek time of an optical head than a high-speed disc drive such as an HDD or the like, the playback video is readily interrupted during seeking fragmented information in the DVD recording/playback system that records/plays back an MPEG moving picture video on/from an optical disc (DVD-RAM disc or the like), resulting in poor practicality of the current system.
When both personal computer data and DVD moving picture data are recorded, fragmentation is more likely to occur. Therefore, the DVD recording/playback system that includes the personal computer environment has no feasibility unless a very high-speed optical disc drive is developed, and a large-size buffer can be mounted at practical cost.
On the medium that records video information (cells), upon repeating editing and partial deletion of recorded information, individual pieces of video information lie scattered or straggle on the medium. When such scattered or straggling video information group is to be continuously played back according to a specific order, frequent accesses are required. During these accesses, since a recorded information group (a series of cells) cannot be played back from the medium, playback is interrupted.
That is, when a specific playback device (disc drive) plays back a scattered or straggling video information group while making frequent accesses, if the access frequency has exceeded a specific number of times, it becomes impossible (for that drive) to continuously output recorded information, thus disturbing seamless playback (without any interrupt).
Furthermore, the frequency shift of the reference clocks of a normal digital audio recorder is approximately 0.1%. When sound source information digitally recorded by a digital video tape (DAT) recorder is overdubbed on video information already recorded on a DVD-RAM disc by digital copy, the reference clocks between the video information and audio information may have an error of around 0.1%. Such reference clock error becomes so large that it cannot be ignored upon repeating the digital copy (or nonlinear edit using a personal computer or the like), and appears as interrupted playback tones or a phase shift between playback channels.
In some cases, audio information corresponding to a specific video pack is stored in an audio pack at a location largely separated from that video pack. When a specific cell is re-recorded at another location on an information storage medium, synchronization between video and audio packs fails if packs under specific cells are simply moved. When playback is made after recording, playback tones are interrupted at that portion.
3. Objects
It is the first object of the present invention to provide an information storage medium capable of real-time recording/real-time playback of digital moving picture information, and a digital information recording/playback apparatus using this medium.
It is the second object of the present invention to provide an information storage medium capable of seamless, continuous playback free from any interrupt by managing the access frequency to a scattered or straggling recorded information group in correspondence with the access performance of the playback device (disc drive) used, and a digital information recording/playback apparatus using this medium.
It is the third object of the present invention to provide an information storage medium which has special synchronization information so that video information and audio information can be synchronously played back (or inter-channel phase synchronization of multi-channel audio information can be taken) even when the reference clocks of the audio information have any error, and a digital information recording/playback apparatus using this medium.
It is the fourth object of the present invention to provide a digital information recording/playback system which can prevent playback information from being lost (sound interrupt or the like) upon playing back specific information, the recording position of which has been changed, when the recording position of the specific information (specific cell) in, e.g., video information, has been changed by, e.g., an edit process of information recorded on an information storage medium.